There have come widely used in recent years a variety of cards represented by licenses such as driver's licenses, identification cards, membership cards with a photograph, certification cards and name cards with a photograph.
On the surface of these cards, or image receiving bodies, an image of the owner's face is often formed for identification. Since such an image of a person's face has gradation, it is also referred to as a gradation containing image. Such a gradation containing image,is not limited to an image of a person's face, and as long as an image has gradation, it is called a gradation containing image.
It is well known that an image formed of a sublimation dye can be improved in fixedness and color tone by subjecting it to surface heat treatment. As a typical conventional technique for such heat treatment, Japanese Pat. O.P.I. Pub. No. 55870/1992 proposes to carry out heat treatment, after thermally transferring a sublimation dye from a transfer sheet onto an image receiving element using a thermal head, by applying heat to the image surface through dye-unapplied portions of the transfer sheet using the same thermal head as the above. However, conducting image formation with a sublimation dye and heat treatment of a resulting image using the same thermal head has a disadvantage of requiring a longer processing time, because a sheet carrying a thermally transferred image has to be turned back again in the reverse direction for each image to receive heat treatment. Further, in carrying out heat treatment, the heat energy applied to a thermal head is greater than that appropriate to form an image effectively; therefore, the heating resistor of such a thermal head cannot be cooled adequately after the heat treatment and thereby accumulates heat in continuous processing. When a thermally transferred image is formed using such a heat accumulating thermal head, heat energy is excessively applied to unnecessary portions of an image forming area, producing unnecessary densities, or so called fog, in the high light portions of an image. This is another disadvantage involved in this technique.
Further, for the purpose of protecting an image formed, there are known a technique to conduct thermal transfer of a transparent resin film onto an image as well as a technique to form a cured resin coating on an image by coating an active energy ray curable resin and irradiating it with a necessary amount of active energy rays. The latter technique has advantages of providing good scratching resistance and solvent resistance, but it has a problem that when an active energy ray curing resin layer is provided on an image formed of a sublimation dye, the combination of the dye and the active energy ray curable resin affects curing properties of the layer, causing a large drop in curing speed or curing failure.
For example, when a cation-polymerizable epoxy-type ultraviolet-curable resin is coated on an image formed of an anionic sublimation dye, the dye inhibits the polymerization under the irradiation of ultraviolet rays, lowering the reaction speed and thereby giving an inadequately cured coating.